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Smoking nests

HOW urbanisation is eating into pristine wildlife habitats and leading to decline in animal populations across the globe has left ecologists worried. Despite this, it seems nature is one step ahead of us in some ways. Scientists from the National Autonomous University of Mexico have discovered what may be a surprising twist of adaptation. They have found that birds in urban areas are using smoked cigarette butts in their nests, probably to exploit the insect-repellent properties of nicotine found in the cigarettes.

Parasitic insects are a nuisance to bird health and a variety of them cohabit with their feathered hosts. They can kill nestlings and force birds to abandon their nests. Parasites, like ticks and lice, feed on blood, weakening the birds and making them susceptible to diseases. Birds have evolved certain defense mechanisms, such as self-medication, to deal with this. ‘Anting’ is one such method where birds rub insects on their feathers. This coats them with anti-parasitic chemicals present in the body of the insects. Lining nests with leaves of aromatic plants is another way to ward off insects. Certain organic compounds, like terpenes, present in these plants are thought to repel parasites, or stimulate the immune system of the chicks.

This is the first time that birds have been reported using cigarette butts in their nests, and the researchers believe it may be a new form of self-medication. But they fear prolonged exposure to toxins in the butts might impact birds’ health in the long run.

For their study, published online in Biology Letters on December 5, they collected around 30 nests each of house finches and house sparrows. Upon comparing the total number of parasitic mites to the amount of cellulose fibre from cigarette butts used in the nest, they found that nests with higher amount of fibre had lesser numbers of mites. This suggests that cigarette butts in the nests might be repelling the mites.

Additionally, they placed both smoked and non-smoked cigarette butts in other nests, which fledglings had recently left. They observed mites show a preference for non-smoked butts, probably because of toxic substances other than nicotine present in smoked ones. The researchers point out the next step is to see if birds prefer using smoked cigarettes into their nests over unsmoked ones. Without this information it is not possible to know if they are picking cigarettes for insect-repellant properties or to make nest bottom soft and insulated. “If it turns out that birds are deliberately choosing smoked cigarette butts, then a fascinating question would be how they ‘know’ these butts have anti-parasitic properties,” says Suhel Quader, an expert on birds at the National Centre for Biological Sciences, Bangalore.

Michael Singer, an evolutionary ecologist at Wesleyan University, Connecticut, considers this behaviour an adaptation to urbanisation more than evolution. “I suspect it is an example of behavioural flexibility rather than evolutionary novelty.”

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